The invention relates generally to pressure sensors and more specifically concerns apparatus for correcting thermal errors in multiple pressure sensor systems.
The major impediment of the widespread use of semiconductor type pressure sensors in the past has been their sensitivity to temperature. This sensitivity to temperature manifests itself as errors that result from changes in zero offset (voltage offset at zero pressure) and in pressure sensitivity. The errors can be reduced by the use of compensating elements or through "in situ" calibration (U.S. Pat. No. 4,111,058), but only at the expense of size, cost, or complexity. The compensating elements are often larger than the pressure sensing elements and require extensive calibration of the pressure sensors before the proper compensating elements can be chosen, thus adding significantly to the cost. Also, because the thermal zero shift is often very nonlinear with temperature, compensating elements generally only are able to reduce the errors to 0.5% full scale per 55.degree. C. For pressure sensors that can be calibrated "in situ," the calibration mechanism is as large as the pressure sensing module and requires pneumatic multiplexing and the generation and accurate measurement of the calibration pressures as well as automatic data processing equipment to compute and store the calibration coefficients.
It is the primary object of this invention to provide a pressure sensing device that largely overcomes the drawbacks of the above mentioned systems.
Another object of this invention is to provide a pressure sensing device that will accommodate multiple pressures, have a high data rate, and high accuracy through the use of analog and digital electronic circuitry that will automatically correct for errors resulting from temperature changes.
Other objects and advantages will become apparent hereinafter in the specifications and drawings.